Questions and Answers
What is the primary cause of Turner’s syndrome?
Which of the following characteristics is associated with Klinefelter syndrome?
What defines a mosaic individual in terms of chromosomal anomalies?
Which of the following best describes a Robertsonian translocation?
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Which type of cellular event typically leads to numerical mosaic anomalies?
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How are mosaic individuals denoted in genetic notation?
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What is a key difference between mosaicism and chimerism?
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Which type of structural chromosomal anomaly is associated with chronic myelogenous leukemia (CML)?
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What is the phenotypic outcome of individuals with Robertsonian translocation?
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What occurs during prophase of mitosis?
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What type of chromosomal anomaly entails the loss of a segment from a chromosome?
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What is the consequence of non-disjunction during meiosis?
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Which chromosomal abnormality is characterized by having an extra chromosome?
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During which phase do chromosomes align at the equatorial plane in mitosis?
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What defines Turner’s syndrome in terms of chromosomal composition?
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What is the outcome of non-disjunction during the first meiotic division?
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What type of offspring results from fertilization involving a normal gamete and a gamete with an extra autosome?
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What happens during anaphase of mitosis?
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Which of these statements is true regarding meiosis?
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Which of the following is a characteristic feature of Down syndrome?
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Which chromosomal abnormality is categorized as a structural anomaly?
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Which phase follows telophase during the mitotic cell cycle?
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What typically increases the incidence of trisomy 21?
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What is the primary purpose of the mitotic spindle during mitosis?
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Which of the following is NOT a common anomaly associated with Edward's syndrome (Trisomy 18)?
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How is Patau syndrome (Trisomy 13) primarily linked to chromosomal abnormalities?
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What is a unique aspect of a nullosomic gamete?
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Which karyotype corresponds to Down syndrome?
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Which of the following statements is true regarding numerical chromosomal anomalies?
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What is the typical outcome for infants born with Patau syndrome?
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What type of chromosomal deletion involves the loss of a segment of chromosome without any attached genetic material at the ends?
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Which karyotype notation indicates a deletion occurring between specific breakpoints within a chromosome?
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What type of chromosomal rearrangement is characterized by a segment of a chromosome breaking off and reinserting itself at the same chromosome but in reverse order?
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How are isochromosomes formed?
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Which statement accurately describes ring chromosomes?
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What is the outcome of nondisjunction during meiotic division?
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What distinguishes mosaicism from chimerism in genetic abnormalities?
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Which type of chromosomal abnormality includes both balanced and unbalanced forms?
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What is a characteristic feature of pericentric inversions?
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What is indicated by the karyotype notation 46,XY,del(7)(q11.23q21.2)?
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Study Notes
Mitosis & Meiosis
- Mitosis consists of a cell cycle with G1, S, and G2 phases; interphase precedes division.
- G1 phase contains one diploid cell; in the S phase, DNA is duplicated forming two sister chromatids.
- G2 phase prepares chromosomes for condensation; two daughter cells produced carry equal genetic information.
- Mitosis phases include:
- Prophase: Mitotic spindle forms, centrosomes pair.
- Prometaphase: Nuclear membrane dissolves, chromosomes attach to spindle microtubules.
- Metaphase: Chromosomes align at the equator.
- Anaphase: Sister chromatids separate at centromeres.
- Telophase: Chromosomes de-condense, nuclear membranes reform.
Non-disjunction and its Impact on Meiosis
- Non-disjunction refers to the failure of chromosomes to separate properly during meiosis.
- This leads to aneuploidy, the presence of an abnormal number of chromosomes in a cell.
- Non-disjunction can occur in:
- Meiosis I: Leads to four unbalanced gametes.
- Meiosis II: Results in two normal and two unbalanced gametes.
- Resultant gametes can produce monosomic (missing one chromosome) or trisomic (extra chromosome) offspring.
Classifications of Chromosomal Abnormalities
- Chromosomal anomalies can be classified into numerical and structural abnormalities.
- Numerical abnormalities alter complete haploid sets (n) of chromosomes.
- Structural abnormalities affect chromosome structure and organization.
Numerical Chromosomal Anomalies
-
Down Syndrome (Trisomy 21):
- Karyotype: 47, XY, +21.
- Most cases result from maternal non-disjunction; incidence rises with maternal age.
- Symptoms: Facial dysmorphology, intellectual disability (IQ < 50).
-
Edward's Syndrome (Trisomy 18):
- Karyotype: 47, XY, +18.
- Occurs in approximately 1 in 6,000 live births; high mortality in infancy.
- Common anomalies: Heart defects, kidney malformations.
-
Patau Syndrome (Trisomy 13):
- Karyotype: 47, XY, +13.
- Half of affected individuals die within the first month; limited survival beyond one year.
- Presents multiple dysmorphic features.
Numerical Sex Chromosome Anomalies
-
Turner's Syndrome (Monosomy X):
- Karyotype: 45,XO; occurs in 1 in 4,000 females.
- The only viable monosomy; traits include short stature and webbed neck.
-
Klinefelter Syndrome:
- Karyotype: 47, XXY; affects about 1 in 600 males.
- Results from nondisjunction during maternal meiosis I; symptoms include breast enlargement and sterility.
Mosaicism
- Defined as the presence of genetically distinct cell lines derived from a single zygote.
- Denoted in karyotypes (e.g., 46, XY / 47, XY, +21).
- Caused by mitotic non-disjunction; not to be confused with chimerism (from multiple zygotes).
Structural Chromosomal Anomalies
-
Reciprocal Translocation:
- Involves exchange between two non-homologous chromosomes (e.g., Philadelphia chromosome linked to CML).
-
Robertsonian Translocation:
- Loss of short arms from acrocentric chromosomes, resulting in fusion of long arms; carriers have 45 chromosomes.
-
Deletion:
- Refers to the loss of chromosome segments; indicated as "del" in nomenclature.
-
Inversion:
- Involves segments breaking and rejoining; categorized as pericentric or paracentric.
-
Isochromosome:
- Occurs when centromeres divide transversely, resulting in chromosome duplication along one arm.
-
Ring Chromosome:
- Formed when breaks on each arm reunite as a ring structure; often unstable in mitosis.
Take Home Message
- Chromosome abnormalities can be classified into numerical and structural, impacting genetic stability.
- Normal meiosis results in four haploid gametes; non-disjunction leads to trisomy or monosomy.
- Mosaicism arises from a single zygote; chimerism from fusion of multiple zygotes.
- Structural abnormalities include various rearrangements, each affecting genetic expression differently.
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Description
This quiz covers key concepts related to chromosome anomalies, focusing on mitosis and meiosis events. It examines non-disjunction and its consequences, as well as various chromosomal abnormalities, including numerical and structural categories. Students will also explore common disorders like trisomies and Turner’s syndrome.
